Continual flow rapid thermal processing apparatus and method

ABSTRACT

A rapid thermal processing apparatus and a method of using such apparatus for the continuous heat treatment of at least one workpiece, which apparatus includes a cavity of generally elongated shape, a process chamber defined by interior walls inside the cavity, a device for delivering, regulating and extracting process gases from the chamber, a device for transporting at least one workpiece through the chamber in a substantially forward direction, a device for heating at least a section of the chamber, and a device for cooling the at least one workpiece downstream from the heating device. The cavity for the apparatus may also be provided in either a curved or a linear configuration for carrying out the present invention method.

FIELD OF THE INVENTION

The present invention generally relates to a method and an apparatus forthe rapid thermal processing of at least one workpiece and moreparticularly, relates to a method and an apparatus for the rapid thermalprocessing of at least one workpiece which can be rapidly heated/cooledby exposing the workpiece to a time dependent, continuous convolution ofnearly black body distributions of electromagnetic radiation in thepresence of processing gases or in vacuum.

BACKGROUND OF THE INVENTION

In the high volume fabrication of semiconductor integrated circuitdevices, the technique of rapid thermal processing (RTP) or rapidthermal annealing (RTA) has become an important processing step in thefabrication of IC devices. In a conventional RTP process, a workpiece isheated by a heat source such as a plurality of tungsten-halogen lamps orarc lamps which provides almost instant heating effect on a workpiecesuch as a semiconducting substrate in the shape of a wafer In most RTPmethods, the heat treatment of a wafer takes place in a single processchamber with the appropriate process gas flow and composition.

A typical single-wafer RTP chamber 10 is shown in FIG. 1A. In RTPchamber 10, an outer chamber wall 12 made of metal is cooled by ambientair and liquid circulating in cooling channels 14. The wafer 18 and thewafer supports 20 are situated inside a fused silica inner chamber wall24 equipped with a process gas inlet 26 and outlet 28. The wafer 18supported by the fused silica supports 20 is heated radiatively by banksof lamps 22 of either tungsten-halogen or arc-type lamps.

The mode of heating provided by the RTP chamber 10 shown in FIG. 1A isdynamic in that the wafer never reaches thermal equilibrium with theheating elements. As a result, the temperature uniformity over the wafersurface depends on the heating rate of the wafer. Furthermore, theradiative coupling between the wafer and the heating lamps variesgreatly with temperature due to the fact that the emissivity of silicondepends strongly on temperature up to about 700° C. In addition, theradiative coupling depends on the physical state of the wafer front andback surfaces. During a typical RTP process as that shown in FIG. 1A,the wafer 18 is heated on both the top and the bottom surfaces and heatfrom the wafer radiates to cold wall surfaces. Based on thissimultaneous heating and cooling, the rate of wafer heating and thewafer final temperature depend strongly on the wafer emissivity, whichis in turn a strong function of the wafer surface structure, the waferbackside textures film stack, and wafer temperature.

Another conventional lamp based RTP chamber 30 is shown in FIG. 1B. Inthis chamber design, a semiconductor wafer 32 to be processed is placedon a susceptor 34 which can be raised up or down by an elevator 36. Thelamp heaters 40 which are enclosed in a reflective dome 42 directradiative energy toward the wafer 44. Process gases are pumped intochamber 46 through gas inlet 48 and exhausted through outlet 52. Itshould be noted that, unlike the chamber construction shown in FIG. 1A,the susceptor 34 is heated simultaneously with the wafer and aids inachieving temperature uniformity across the workpiece.

The present trends in semiconductor manufacturing indicate that in thenear future the wafer heating rate and cooling rate will increase andthat the time interval during which a wafer is maintained at a desiredpeak temperature will decrease substantially. The trends are dictated byhigh performance logic circuits that are based on very shallow junctionsthat must be prepared in a fabrication process with stringent thermalbudget limitations. Moreover, in today's highly competitive environment,the manufacturing of semiconductor devices continues to strive forefficiency and throughput gains and thus, a more uniform and higherthroughput RTP process is desired.

Conventional RTP chambers such as those shown in FIGS. 1A and 1B haveperformance limitations that limit their ability to meet futurerequirements of significantly faster heating rates. On the one hand,from a performance consideration, the ramp rate of conventional RTPchambers is limited by the requirement of temperature uniformity in thehighly transient environment of conventional RTP chambers, which requirefeed-back control and independently addressable lamps in order toachieve an acceptable degree of temperature uniformity across the waferworkpiece. On the other hand, at the outer limits of tool performancethe rate at which the wafer of a given size can be heated is limited bythe time it takes for the lamp filament to achieve operationaltemperature and furthermore, by the radiant flux at the wafer. Thelatter is limited by how closely the heating lamps can be stackedtogether and the maximum radiant power flux of each lamp which islimited by the melting point of the tungsten filament and the softeningpoint of the lamp's conventional fused silica enclosure. It has beenfound that the maximum achievable heating rate for an industry standardsilicon wafer of 200 mm diameter in a conventional, lamp-based RTPchamber is limited to about 150° C./sec.

In recent years, RTP has also been conducted in vertical hot wallfurnace-type chambers in limited applications. One of such devices isshown in FIG. 1C. A hot wall RTP furnace 50 is closed on all but oneside (the bottom) through which wafers 54 are introduced andsubsequently removed from the furnace upon completion of the thermalcycling treatment. The hot wall RTP furnace 50 has a vertical axis alongwhich the wafers move by the action of elevator 66 on a wafer carrier 46while maintaining the plane of the wafers perpendicular to the verticalaxis of the chamber 50. The furnace 50 is closed at the top and isequipped with a top heater 58, and closed on the sides where side upperheaters 62 are mounted thereto. The furnace 50 has a chamber 64 definedby a fused silica chamber wall 76 and may include additional heatingzones 68, each of which is maintained at a specific temperature. Thewafers 54, positioned on wafer carrier 46 can be moved into or out ofthe chamber 64 by an elevator 66. The chamber 64 is further heated bylower side heaters 68 to facilitate the control of chamber temperature.Various process gases may enter the chamber 64 through gas inlet 72 andbe exhausted from the chamber through gas outlet 74. During operation,wafers 54 are slowly transported vertically through one or moretemperature zones coming to a full stop at a desirable location wherethe wafers achieve a temperature that is much less (100-500° C.) thanthat of the surrounding hot walls. After a suitable amount of time whichmay vary from several seconds to several minutes, the wafers can bewithdrawn and allowed to cool. Limited by its basic design, the existinghot wall RTP furnace cannot achieve very high heating rates and shortdwell times at a desirable wafer temperature.

Neither the lamp-based nor the hot wall-based RTP furnaces that arepresently available can be used to process large workpieces (or wafers)at heating rates that are much higher than 150° C./sec and at dwelltimes at peak temperatures that are much shorter than one second.Therefore, prevailing art in current practice cannot meet the processingrequirements for high performance logic circuits.

It is therefore an object of the present invention to provide a methodand an apparatus for RTP that does not have the drawbacks andshortcomings of conventional lamp-based or hot wall-based RTP furnaces.

It is another object of the present invention to provide a method and anapparatus for RTP in which the temperature of at least one workpiece canbe increased and decreased uniformly at rates that are much greater than150° C./sec.

It is a further object of the present invention to provide a method andan apparatus for RTP which can be used to provide similar heating andcooling rates to wafers that are of common industrial sizes of 125 mm,200 mm, 250 mm or 300 mm in diameter.

It is yet another object of the present invention to provide a methodand an apparatus for RTP in which at least one workpiece can be rapidlyheated, in the presence of processing gases or vacuum, by a single heatpulse of short temporal duration.

It is still another object of the present invention to provide a methodand an apparatus for RTP in which the temperature of at least oneworkpiece can be maintained substantially uniform during rapidtemperature cycling.

It is still another further object of the present invention to providean apparatus for RTP which has a curved, horizontally oriented cavitystructure that supports a plurality of zones with walls that aremaintained at working temperatures.

It is yet another further object of the present invention to provide amethod and an apparatus for RTP which utilizes a transport mechanismthat is capable of carrying one or more workpieces unidirectionallythrough a horizontal processing chamber within a curved or linearcavity.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and an apparatus forRTP are provided wherein the temperature for at least one homogeneousworkpiece can be increased and decreased uniformly at rates that aremuch greater than 150° C. per second without the drawbacks andshortcomings of conventional RTP methods.

In a preferred embodiment, the present invention provides a rapidthermal processing apparatus consisting of a curved cavity that supportsa plurality of zones with walls that are maintained at workingtemperatures, a processing chamber within the cavity, a means fordelivering, regulating and extracting process gases from the chamber, atransport mechanism that carries at least one workpiece through theprocessing chamber, and a zone for rapid cooling. A rapid thermalprocessing method can be carried out by first placing at least one waferin a carrier within the loading zone at one end of the processingchamber. The reaction chamber is purged of unwanted gases and processgases are introduced into the chamber. The wafer carrier is subjected toa controlled forward motion along the reaction chamber and travelsthrough various zones that are maintained at desired temperatures at alltimes. The processed wafer then enters a cooling zone section of theprocessing chamber and is finally extracted in the unloading zone at theopposite end of the curved cavity. The wafer is exposed to a temperatureexcursion having characteristics that are determined by the transportspeed, the temperature of each zone, the emissivity of the wafer, and tosome extent the ambient gas. An uniform heating of the wafer iscontrolled by the curved shape of the cavity, the interior wall texturedesign, the cavity diameter in relation to the diameter of the wafer,and the orientation of the wafer surface in relation to the axis of thecavity.

The present invention is a continuous flow, rapid thermal processingcavity that can be used to manufacture semiconductor devices that arebuilt on semiconducting wafer substrates of any diameter such as thosecommonly seen in the manufacture of memory and logic circuits used inmost advanced digital computers. The RTP cavity provided by the presentinvention enables the manufacture of advanced memory and logic circuitsfor which manufacturing and design specifications require fast heatingand cooling rates and impose severe limits on the convolution oftemperature and time-at-temperature over the entire manufacturing cycle.

The present invention continuous flow RTP cavity is therebycharacterized by very fast heating and cooling rates in comparison towhat is presently available while maintaining a substantial degree oftemperature uniformity over the workpiece, and a substantial degree ofreproducability, short cycle time and high throughput. The presentinvention apparatus is further characterized by the transient heatingand cooling of the workpiece in a hot wall reactor in which theworkpiece is never allowed to approach near thermal equilibrium with hotwalls of the processing cavity, and is further characterized by acontinuous, forward motion of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

FIG. 1A is a schematic illustrating a cross-sectional view of aconventional lamp based RTP apparatus.

FIG. 1B is a schematic illustrating a cross-sectional view of anotherconventional lamp based RTP apparatus.

FIG. 1C is a schematic illustrating a cross-sectional view of aconventional furnace based RTP apparatus.

FIG. 2A is a partial perspective view with partial broken away sectionalviews of a curved section of the present invention RTP apparatus.

FIG. 2B is a side cross-sectional view of the RTP apparatus of FIG. 2Ashowing the transporting means for wafers and the heating and coolingzones.

FIG. 2C is an end cross-sectional view of the curved cavity of thepresent invention RTP apparatus showing a detailed transport mechanism.

FIG. 2D is a side view of a wafer-transporting carrier for the presentinvention apparatus.

FIG. 3A is a plan, top view showing the curved cavity in relation toloading and unloading zones and a wafer carrier means.

FIG. 3B is an end cross-sectional view of the curved cavity of thepresent invention RTP apparatus of FIG. 3A showing a second embodimentof a wafer being carried by the wafer carrier.

FIG. 3C is a side view of the wafer carrier shown in FIG. 3B.

FIG. 3D is a partial perspective view of the RTP apparatus of FIG. 2Bshowing the wafer carrier platform and the guide rollers of FIGS. 3A and3B.

FIG. 4A is a side cross-sectional view of the present invention RTPapparatus in a second embodiment utilizing a linear instead of curvedcavity and a cable transport for workpiece.

FIG. 4B is an end cross-sectional view of the linear cavity of FIG. 4Ashowing a third embodiment of the wafer carrier.

FIG. 4C is a perspective view of the wafer carrier shown in FIG. 4A.

DETAILED DESCRIPTION OF THE PREFERRED AND THE ALTERNATE EMBODIMENTS

The present invention provides a novel rapid thermal process apparatusand a method for using such apparatus in the heat treatment of at leastone wafer. The method is characterized by very fast heating and coolingrates when compared to conventional RTP apparatus while maintaining asubstantial degree of temperature uniformity over the wafer, asubstantial reproducibility, short cycle time and high throughput. Thepresent invention method is further characterized by the transientheating and cooling of wafers in a hot wall reactor in which the wafersare never allowed to approach near thermal equilibrium with hot walls ofthe RTP cavity.

The present invention provides a novel hot wall, continuous flow, rapidthermal process reactor for processing not only a single workpiece, butalso a plurality of workpieces. The novel continuous flow RTP provides aheating rate that is much higher compared to the heating rate possiblein a conventional reactor, i.e., a rate between about 1° C./sec andabout 5000° C./sec. The rapid heating rate achievable by the presentinvention is one of the major advantages when used in the manufacture ofhigh performance semiconductor devices which requires shallow junctionsin a process of restricted thermal budget. Such semiconductor devicesare frequently fabricated on silicon wafers of any suitable size, i.e.,a diameter of 200 mm, 300 mm or any other diameters that can be used inthe semiconductor industry for the manufacture of integrated circuit(IC) devices such as for logic or memory. The present invention novelreactor is capable of processing a plurality of wafers together in acontinuous fashion where the distance required between wafers is muchless than the radius of a wafer. The present invention novel reactor canalso process a single wafer, or a continuous succession of single wafersthat are separated by a suitable distance that is much larger than thediameter of a wafer. For instance, in the preferred embodiment, a singlewafer is processed individually. However, a batch of wafers together ora sequence of wafers positioned at close intervals could be processedusing the same reactor but a different wafer transport mechanism basedon the alternate embodiments of the invention. In one alternateembodiment, a present invention continuous flow RTP reactor is capableof processing a sequence of four wafers that are spaced apart by severaldiameters length but are carried simultaneously by the same transportmechanism.

Referring initially to FIG. 2A which shows a perspective view of thepresent invention curved cavity RTP reactor 80 with partiallybroken-away sections. The apparatus 80 is shown with a geometry that isessentially toroidal or curved and is equipped with a number of hot wallregions 82, 84 and 86 with the desired distribution of internal walltemperature. The apparatus 80 is further equipped with a cooling region88 for the rapid extraction of heat from workpiece 90 after processing.

As shown in FIG. 2A, the continuous flow RTP reactor 80 is constructedmainly of a toroidal or curved cavity that has an inner wall 94, anouter wall 96, an entrance opening 98 for introducing wafers into thecavity 100 and an exit opening 102 for removing processed wafers fromthe reactor. Along a section of cavity 100 high temperature zones 82-86that have interior wall temperatures preset according to processingspecifications. It should be noted that the cross-section of cavity 100may be circular, rectangular or any other desirable shape. The cavity100 may have its axis (not shown) oriented at any angle with respect tothe vertical. The axis (not shown) of cavity 100 may be curved, i.e.,may in fact be a portion of a toroid or other geometrical shape, or maybe linear. Internal to cavity 100, a liner or inner wall 94 which hasinterior walls equipped with a relief geometrical pattern or baffledgeometrical pattern (not shown) for the purpose of adjusting radiativeheat exchange with the workpiece. At or near the exit opening 102, anddownstream from the heating zones 82-86 is a cooling zone 88 wherewafers are cooled prior to removal from the continuous RTP reactorcavity 80. The rapid cooling zone 88 mounted on the inner liner 94 maybe constructed of an optically transparent envelope (not shown) whichcarries a fluid having a high emissivity. For instance, a fluid mayconsist of colloidal suspension of fine carbon particles.

The cavity 80 is further equipped with a number of orifices 112 and 114for the purpose of introducing gases of various compositions through gasinlet conduit 108, gas outlet conduit 106, flow controller 116 and anexternal gas supply 110.

The heating of the cavity 80 at the heating zones 82-86 can be achievedby supplying a thermal energy source for each zone. Such source ofthermal energy may be as a result of passing an electrical current (ACor DC) through conduits that resist flow of electrical charge, or as aresult of causing rapidly alternating currents to flow, as by means ofradio frequency (RF) induction, in some zones that are constructed froma partly conducting material such as pyrolitic graphite, or as a resultof circulating a liquid (for example, a liquid metal or other liquid) atthe desired temperature through hollow conduits or channels, or a resultof gas flow (for example, steam, superheated steam or any gas used forthe purpose of transferring heat) at the desired temperature throughhollow conduits, or as a result of exothermic chemical reaction methods(for example, controlled oxidation of methane, acetylene, or hydrogen)within conduits to produce the desired temperature in the specificheating zone.

The heating zone 82-86 can be constructed of materials that have a highmelting or sublimation temperature among which, are (listed with theirrespective melting temperatures in °C.): HfC (3928), TaC (2983), C(3800), ZrC (3420), TaN (3440), W (3380), TiC (3067), NbC (3600), andHfN (3387). Other portions of the reactor cavity 80 can be constructedof other materials (listed with their melting temperature in °C.): NbB₂(2900), B (2300), CaO₂ (2500), MgO (2800), TiN (2950), TiB (2900), NbN(2500), and MoC (2700).

As shown in FIG. 2A, an energy source 122 such as an electrical currentprovides energy to the high temperature zone 82-86 by passing thecurrent through a conduit that resists motion of electrons. Atemperature regulating means for maintaining each of the heating zonesat a predetermined temperature consists of suitable sensors 124 (forexample, a thermocouple sensor, a gas pressure sensor, a resistivesensor, an eutectic sensor, a capacitive sensor, an inductive sensor, oran oscillating element whose frequency depends on temperature) and atemperature controller 126. A feedback controller 128 is also used toregulate the temperatures of the heating zones 82-86. The temperatureregulating means therefore includes one of the above suggestedtemperature sensors, a temperature controller 126 and a feedbackcontroller 128 for processing the sensor signal and utilizing it in afeedback control to increase or decrease energy flow to the heatingzones such that the temperature of the zone can be maintained within anarrow range.

Between outer wall 96 and outer enclosure 132 and near the heated zones82-86 of the cavity 80, thermal barrier devices (not shown) forminimizing heat energy flow to the environment may be installed whichconsists of a number of radiation barriers (or low emissivity layers), anumber of barriers to heat conduction (such as layers of materials withlow heat conduction capability, or a vacuum layer) and a number ofbarriers to heat transport by convection by eliminating gas pockets. Ageometrical tapering in the internal dimensions of the zones isappropriate for achieving variations in the temperature distributionover the workpiece. A sequence of fins, baffles or reliefs on the innersurfaces of each heating zone which can be oriented at various angles tothe workpiece 90 can also be provided to achieve more or less efficientradiative heat transfer as desired. This enables the workpiece toachieve a more uniform temperature distribution over its entire surface.

A rapid heat extraction zone (or cooling zone) 88 for the rapid coolingof the wafer 90 is provided which consists of high emissivity cold wallinterior surfaces and forced convective cooling from flowing gases. Thecooling zone 88 is controlled by a heat exchanger 134, a coolant flow136 and a high emissivity cooling fluid 138.

An outer protective skin (or outer enclosure) 132 is provided forcontrolling the gaseous environment external and internal cavity 100. Adetailed illustration of the transport system will be shown in FIGS. 2B,2C and 2D.

FIG. 2B is a cross-sectional view of the present invention continuousflow RTP cavity 80 of FIG. 2A. The wafer (or plurality of wafers) 90 iscarried through the cavity 80 on a carrier 150 that rides on rails 140.This is shown in FIG. 2B. Wafers enter the processing cavity at 98 andexit at 102 in a continuous, uninterrupted motion. The transportmechanism for moving the wafers through cavity 80 consists of a railsystem 140 (shown in FIGS. 2B, 2C and 2D), a carrier 150 that rides onrails 140, a wafer paddle 152 which holds the wafer securely in placewhen moved on the carrier and which is mounted to the carrier 150.

The rails 140 may be constructed from a suitable material such astungsten. The carrier 150 and the paddle 152 may be constructed from asuitable material such as fused silica such that these structures, whichare designed only to carry the workpiece, can rise to a temperature thatis much less than that of the workpiece during transit through thecavity 80. The rails 140 may include two or more rails arranged alongthe axis of the cavity 80. A link chain or cable 156, as shown in FIG.2D, with suitable mechanical harness can be used for moving carrier 150.A passive, automatic engagement system (not shown) such as a gravityactivated flap or a retractable hook can be used for engaging ordisengaging the carrier 150 from the rails 140. A separate speed control(not shown) is used to drive the chain or cable which may bepreprogrammed. A rail switching mechanism (not shown) for switchingcarrier 150 from different rail segments such as various wafer loadingstations onto the track can be used so that the wafers can betransported into and out of the continuous flow RTP chamber 80.

FIG. 2B further illustrates the preferred embodiment of the presentinvention continuous flow RTP chamber wherein the cavity inner wallliner 158 is equipped with a textured surface 160 as a relief foruniformity control. Heating zones 82, 84 and 86 are also provided in thecavity inner wall liner 158 which consists of power conduits enclosed inceramic material such as HfC. A barrier 190 to minimize the rate of heattransport from hot zones 82-86 is placed between outer cavity wall 96and outer enclosure 132. A transition section 162 is provided betweenthe heating zones 82-86 and the cooling zone 88. The result of themotion through the heating zones 82-88 of the cavity 80 is that wafer 90experiences a substantially uniform temperature rise whose rate, peakand duration depend solely on the wafer rate of motion, temperatures ofheating zones and emissivity properties of the wafer. The wafer positionand the rate of motion can be sensed by a sensor (not shown) andregulated by a motion regulator (not shown). Finally, the wafer istransported to a cooling zone (or a heat extraction zone) 88 where thewafer experiences a substantially uniform temperature drop at a ratethat is, in part determined by the cooling zone wall temperature and thecooling gas flow rate.

A substantially uniform temperature is a temperature distribution overthe entire wafer that yields process results of an acceptable qualityfor the particular process being performed, for example, annealing afterion implantation may require that the highest and lowest temperatureanywhere across a wafer vary by not more than 3° C. for an average wafertemperature of 1000° C.

It is seen that a textured surface 168 is also provided in the coolingzone 88 for increasing cooling rate of the workpiece. A high emissivityfluid, 138 in FIG. 2A is flown through the cooling zone 88 together witha cooling gas flow 172 for achieving rapid cooling of the wafers. Thecooling gas flow 172 exits the chamber 100 through gas outlet 176.Similarly, a cooling and non-reactive gas flows in the outer environmentbetween outer enclosure 132 and outer cavity 100, entering at 178 andoutflowing at 184. A baffle plate 188 is provided for thermal isolationbetween the heating zones 82-86 and the cooling zone 88, and furtherrestricts cooling gas flow from the cooling zone 88 to the hot region ofthe cavity 100. It should be noted that cavity 80 can be provided eitherin a curved section or in a linear section, but preferably, in atoroidal section.

The movement of wafer 90, positioned at an angle θ with respect to avertical axis, through chamber 100 creates an interaction with the heatwaves emitted from the heating zones 82-86 such that the workpieceexperiences heat impulses consisting of continuous, convolution orsuperposition of impulses of electromagnetic radiation. It has beenproven that within a closed cavity each of the impulses has a spectraldistribution of power that is substantially similar to that of an idealblack body radiator. This is one of the key advantages that are madepossible by the present invention in providing a continuous flow, rapidheating/cooling RTP apparatus and method.

A detailed illustration of the carrier 150, the paddle 152 and the guiderail system 140 is shown in FIGS. 2C and 2D. A wafer 90 is positioned inthe paddle 152 on the carrier 150 at an angle θ from the vertical axis.The angle can be suitably selected between 0 and about 60° to allowheated gas to flow through and around the outer peripheral edge of thewafer 90. The inner wall relief, or a textured surface 160 is providedon the heating zones 82-86 such that a more uniform wafer temperature inthe RTP chamber can be achieved. The wafer holder or paddle 152 can bemade of a thin fused silica material such that it remains at a muchlower temperature than that achieved by the wafer 90. At the upperextremities of the wafer paddle 152, guide rollers 192 (usually providedas a pair) are provided for moving the carrier 150 which rides on theguide rails 195 through the chamber 100. The movement of the carrier 150is controlled by the guide rollers 192, which can also be suitablymanufactured of fused silica, and are mounted to the carrier 150. Adrive pin 198 is provided to the carrier 150 such that it can be engagedto a drive cable 156 for pulling the carrier through the chamber 100when the wheels 194 ride securely on the drive rail 140. It should benoted that the transport mechanism illustrated in FIGS. 2C and 2D ismerely one of many possible embodiments for the transport system in thepresent invention novel continuous flow RTP apparatus.

FIG. 3A is a top view showing a curved cavity similar to that in FIG.2A, but with a second embodiment of a wafer transport mechanism andshowing an embodiment for wafer loading and unloading mechanism. In FIG.3A, a toroidal processing chamber 202 and a wafer carrier 204 forcarrying three or more wafers are provided; four wafers 206-212 arecarried by the carrier 204. A controlled environment enclosure 218 isprovided which completely encompasses the carrier 204, the processingchamber 202, the loading and unloading station 220 equipped with doors222. In the processing chamber 202, heating zones 230-238 of a hot walldesign and cooling zone 254 are utilized to heat/cool the wafers as theypass through the heated/cooled section on the carrier 204. A pluralityof rolling guides 242 are provided for the transport of carrier 204,i.e., a total of seven pairs are shown in FIG. 3A. The wafers are loadedfrom the loading/unloading station 220 by a mechanical robot loader (notshown) onto wafer paddles (not shown) pre-positioned on carrier 204. Awafer 252 is shown in FIG. 3A in the process of being loaded by therobot loader (not shown).

FIG. 3B is a cross-sectional view of the alternate wafer transportembodiment of the continuous flow RTP apparatus 200 shown in FIG. 3A. Inthe processing chamber 202, a wafer 208 is carried by the wafer carrier204 and secured by the wafer paddle 256 and is guided by rolling guides242 that also provide locomotion.

FIG. 3C is an enlarged, side view of the wafer 208 being transported ona carrier 204 and wafer paddle 256. The wafer 208 is mounted such thatits surface lies in a plane that makes an angle θ with the verticalaxis. The paddle 256 is normally constructed of fused silica, aluminumoxide or any other suitable high temperature material. The paddle 256makes a minimal contact with the outer edge of the wafer 208 when thewafer is being transported through the RTP chamber 202. FIG. 3D is aperspective view of the RTP apparatus 200 shown in FIG. 3A showing onlywafer carrier 204 without wafer paddle 256, and guide rollers 242. Itshould be noted that windows 272 are provided in carrier 204 to reduceweight and provide improved gas flow and temperature uniformity insidethe RTP chamber 202.

A second alternate embodiment of the present invention continuous flowRTP apparatus 300 is shown in a cross-sectional view in FIG. 4A. In thissecond alternate embodiment, the RTP cavity is laid out in a linearfashion, instead of in a toroidal shape. The wafer transport is effectedby means of a third embodiment, a top cable 302, a bottom cable 304 anda carrier frame 306 attached to guide tubes 310 through which pass drivecables 302 and 304. The cavity embodiment of FIG. 4A differs from thatof FIGS. 2A or 3A only in that its axis lies in a straight line. Othercomponents such as heating zones 11-15, cooling zone 21, interior wallgeometry 41 gas flow (not shown), outer enclosure, and barrier to heatflow are essentially the same as those described in conjunction withFIGS. 2A and 3A.

In the linear cavity, baffles 31 and 33 are essential to preventextensive heat loss from open ends. FIGS. 4B and 4C shows an endcross-sectional view of the apparatus 300 and a perspective view of thewafer carrier 310, 306, respectively. A wafer 320 is transported on acarrier frame 306 (attached to guide tubes 310 through which pass drivecables 302 and 304) wherein the wafer 320 is mounted in such a way thatits surface lies in a plane that makes an angle θ with the verticalaxis. The wafer 320 is held in a wafer paddle 322 that is fixed to thecarrier frame 306 which is attached to guide tubes 310. The wafercarrier, 322, 306 and 310 can be constructed of fused silica, aluminumoxide or any other suitable high temperature material. The wafer paddle322 makes minimal contact with the outer edge of the wafer 320 when thewafer is transported through the RTP cavity 300 on a top and bottomcable 302 and 304 with the two cables simultaneously pulling the wafercarrier composed of components 306, 310 and 322.

Industrial Applicability

An important aspect of the present invention apparatus is the ability torapidly increase and decrease the temperature of an entire wafer whereinthe wafer temperature remains substantially uniform across its surfaceat all times. The present invention RTP apparatus and method can be usedto perform all of the processes performed by conventional RTP reactors.For instance, all anneal and dopant activation processes can be carriedout in the present invention RTP chambers. It is known that the fractionof dopant activation depends on the time at peak temperature, the dopantspecie, the dopant concentration and the implantation energy, while thediffusion distance of implanted species depends on an integration oftime and temperature, and the dopant specie. For example, when arsenicions, having an energy of 30 keV, are implanted into nominally orientedsilicon with a dose of 10¹⁵ cm⁻², the silicon lattice returns to apredominantly damage-free state and the implanted ions becomepredominantly activated when the implanted silicon is heated to 1080° C.for a period of 20 seconds. The present invention RTP apparatus andmethod provides the ability to reach peak temperatures much more quicklyand with substantially uniform temperature across an entire wafer thanis possible with conventional RTP reactors. The ability to heat theentire wafer very rapidly and uniformly is important for the formationof ultra shallow dopant profiles and for optimizing the overall heatexposure which a wafer undergoes during the entire manufacturing cycle.The ability to raise the wafer temperature quickly to the desiredprocess temperature minimizes exposure of the wafer to lowertemperatures that do not contribute to the process at hand but,nevertheless add to the total amount of heat that a wafer is allowed tobe exposed to during the entire manufacturing cycle.

In addition to annealing, the present invention RTP apparatus and methodcan be used to sinter metal contacts. To achieve a goodmetal-semiconductor contact after deposition, the metal-semiconductorcombination is heated to a temperature at which some interdiffusion andalloying occurs at the metal-semiconductor interface. For example, foraluminum, the temperature is typically in the range between about 430°C. and about 510° C. in either an inert gas atmosphere or in one whichcontains hydrogen for a time that may vary from about 5 to about 30seconds.

In addition to annealing and sintering, the present invention RTPapparatus and method can be used to form ohmic silicide contacts tosilicon devices. In this process, a thin layer of metal is depositedover the wafer and the entire wafer is then heated to form ametal-silicide contact at the interface between the metal film andsilicon while the excess metal is subsequently etched away. Theformation of a metal silicide that has the desired composition andresistivity is dependent upon the heating rate, the formationtemperature and the anneal temperature. For example, refractorymetal-silicide are generally formed by first heating the previouslydeposited thin metal on a silicon carrier to about 700° C. for a periodof about 30 seconds, etching away unused metal and subsequently heatingthe wafer to about 900° C. for about 5 seconds. In addition toannealing, sintering and the formation and annealing of variousmetal-silicon compounds, the present invention RTP apparatus and methodcan be used to form films of various chemical composition, on surfaces,from vapors and gases of various chemical composition and proportionalconcentrations.

As examples, the present invention RTP and method can be used to growsilicon films from silane gas on various surfaces; to grow silicondioxide glass films from dichlorosilane and nitrous oxide gases onvarious surfaces; and silicon nitride from dichlorosilane and ammoniagases on various surfaces.

While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms ofa preferred and alternate embodiment, it is to be appreciated that thoseskilled in the art will readily apply these teachings to other possiblevariations of the inventions.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An apparatus forcontinuous heat treating at least one workpiece comprising:a cavity ofgenerally elongated toroidal shape, a process chamber defined byinterior walls inside said chamber, a means for providing a process gasto said chamber, a means for transporting at least one workpiece throughsaid chamber in a substantially forward direction, a means for loadingand unloading said at least one workpiece into and from saidtransporting means, a means for heating at least a section of saidchamber at a heating rate higher than 150° C./sec, and a means forcooling said at least one workpiece downstream from said heating means.2. An apparatus according to claim 1, wherein said heating means heatssaid at least one workpiece at a heating rate between about 1° C./secand about 5000° C./sec.
 3. An apparatus according to claim 1, whereinsaid cavity of generally elongated shape is curved or linear.
 4. Anapparatus according to claim 1, wherein said cavity of generallyelongated shape is toroidal.
 5. An apparatus according to claim 1further comprising baffle means between said heating means and saidcooling means.
 6. An apparatus according to claim 1, wherein said meansfor providing a process gas to said chamber further includes means toregulate the gas pressure and means to evacuate the gas from thechamber.
 7. An apparatus according to claim 1, wherein said means fortransporting said at least one workpiece includes a carrier for holdingsaid at least one workpiece and a rail system for moving said carrierthrough said chamber.
 8. An apparatus according to claim 7, wherein saidrail system further comprising a cable for pulling said carrier forriding on at least one rail.
 9. An apparatus according to claim 1,wherein said means for heating at least a section of said chambercomprises a heating method selected from the group consisting of passingan electrical current (AC or DC) through conduits that resist flow ofelectrical charge, circulating a high temperature liquid at a desiredtemperature through hollow conduits or channels, flowing a hightemperature heat transferring gas at a desired temperature throughhollow conduits, causing rapidly alternating currents to flow in zonewalls that are constructed from a partly conducting material, andpassing a reaction product of an exothermic chemical reaction withinhollow conduits at a desired temperature.
 10. An apparatus according toclaim 1, wherein said means for cooling said at least one workpiececomprises an optically transparent envelope which carries a fluid havinga high emissivity.
 11. An apparatus according to claim 10, wherein saidfluid having a high emissivity is a fluid consists of colloidalsuspension of fine carbon particles.
 12. An apparatus according to claim1, wherein said interior walls of the process chamber further comprisesthermal barrier devices for minimizing heat transfer to the environment.13. An apparatus according to claim 12, wherein said thermal barrierdevices is selected from the group consisting of a number of lowemissivity radiation barriers, a number of barriers to heat conduction,and a number of barriers to heat transport by convection and byeliminating gas pockets.
 14. An apparatus according to claim 1, whereinsaid means for heating at least a section of said chamber furthercomprises a sequence of fins, baffles or reliefs on the inner surfacesof said heating means.
 15. An apparatus according to claim 14, whereinsaid sequence of fins, baffles or reliefs can be oriented at variousangles to said at least one workpiece for providing more or lessefficient radiative heat transfer.
 16. An apparatus for continuous heattreating at least one workpiece comprising:a cavity of generallyelongated toroidal shape, a process chamber defined by interior wallsinside said cavity, a means for providing a process gas to said chamber,a means for transporting at least one workpiece through said chamber ina substantially forward direction, a means for heating said at least oneworkpiece at a heating rate between about 200° C./sec and about 5000°C./sec, and a means for cooling said at least one workpiece downstreamfrom said heating means.
 17. An apparatus according to claim 16 furthercomprising means for loading and unloading said at least one workpieceinto and from said transporting means.
 18. An apparatus according toclaim 16, wherein said cavity of generally elongated shape is curved orlinear.
 19. An apparatus according to claim 16, wherein said means forheating at least a section of said chamber comprises a heating methodselected from the group consisting of passing an electrical current (ACor DC) through conduits that resist flow of electrical charge,circulating a high temperature liquid at a desired temperature throughhollow conduits or channels, flowing a high temperature heattransferring gas at a desired temperature through hollow conduits,causing rapidly alternating currents to flow in zone walls that areconstructed from a partly conducting material, and passing a reactionproduct of an exothermic chemical reaction within hollow conduits at adesired temperature.